Pairing of Components in a Direct Current Distributed Power Generation System

ABSTRACT

A method of signaling between a photovoltaic module and an inverter module. The inverter module is connected to the photovoltaic module. In an initial mode of operation an initial code is modulated thereby producing an initial signal. The initial signal is transmitted from the inverter module to the photovoltaic module. The initial signal is received by the photovoltaic module. The operating mode is then changed to a normal mode of power conversion, and during the normal mode of operation a control signal is transmitted from the inverter to the photovoltaic module. A control code is demodulated and received from the control signal. The control code is compared with the initial code producing a comparison. The control command of the control signal is validated as a valid control command from the inverter module with the control command only acted upon when the comparison is a positive comparison.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of pending U.S. patentapplication Ser. No. 12/329,525 filed on Dec. 5, 2008 by the presentinventors the disclosure of which is included herein by reference. Thepresent application claims priority from pending U.S. patent applicationSer. No. 12/788,066 filed on May 26, 2010.

FIELD AND BACKGROUND 1. Field

The present invention relates to power generation systems, andspecifically to a system and method for reducing crosstalk whilesignaling between the components in direct current distributed powergeneration systems.

2. Related Art

A photovoltaic power generation system may incorporate one or morephotovoltaic panels with optional electronic modules attached thereto.An inverter connects to the photovoltaic panels or electronic modules.Power output from the photovoltaic panels or electronic modules isdirect current (DC) power. The electronic modules may perform directcurrent DC-to-DC conversion. The inverter inverts the DC power output toalternating current (AC) power.

As previously disclosed by the present inventors in US patentapplication publication 2008/0147335, the DC power cables connectinginverters to photovoltaic panels and/or electronic modules may provide acommunication channel between the inverters and the photovoltaic panelsor modules. The communication channel between inverters and modules,allows monitoring of the performance of the modules for monitoringtemperature, current, voltage and power output of the photovoltaicmodules and potentially allows for control of the modules.

Typically, lengths of cables connecting the inverter to the panels ormodules may be long and may contain one or several wire cores. Within aphotovoltaic installation, a wire at positive potential and a wire atnegative potential electrically associated therewith may be physicallyproximate thereto only at a point of connection to a piece of equipment.However, elsewhere in the photovoltaic field, the wires may be separatedand not be within the same cable run. The topography of the distributedpower generation system to a large extent dictates the installation andplacement of cable runs. Physical proximity of wires not having anelectrical association may increase the chances of the wires in thecables being subject to the effects of noise if those wires are to beconsidered for signaling by DC power line communications. Crosstalk is atype of noise which refers to any phenomenon by which a signaltransmitted on a cable, circuit or channel of a transmission systemcreates an undesired effect in another cable, circuit or channel.Crosstalk is usually caused by undesired capacitive, inductive, orconductive coupling from one cable, circuit or channel, to another.Crosstalk may also corrupt the data being transmitted. Typical knownmethods of preventing the undesirable effects of crosstalk may be toutilize the shielding of cables, modules, panels, inverters or usingtwisted pair cables. Additionally, filtering techniques such as matchedfilters, de-coupling capacitors or chokes may be used to prevent theundesirable effects of crosstalk. However, these typical ways ofpreventing the undesirable effects of crosstalk are typicallyunavailable or impractical for power line communications over DC linesin a power generation system and/or may be prohibitively expensive interms of additional materials and/or components required.

In a photovoltaic power generation system, with power line communicationover DC cables, it may be desirable to send a control signal between andan inverter and a particular photovoltaic module but no other modules.Crosstalk may cause the other photovoltaic modules in the powergeneration system to inadvertently receive the control signal which isof course undesirable.

Thus there is a need for and it would be advantageous to have a systemand method of reducing cross-talk in DC power line communications in adistributed DC power generation system, e.g photovoltaic DC powergeneration system.

The term “memory” as used herein refers to one or more of programmableread only memory (PROM), erasable programmable read only memory (EPROM),electrically erasable programmable read only memory (EEPROM), FLASHmemory, optical memory, e.g. compact disk, switches, random accessmemory (RAM), magnetic memory such as a hard disk or other memory typesknown in the art.

The term “direct current (DC) power source” as used herein refers to(DC) power source such as batteries, DC motor generator; switch modepower supply (SMPS), photovoltaic panels and/or photovoltaic panelsoperatively attached to a converter module such as a DC to DC converter.

The term “photovoltaic source” as used herein refers to a photovoltaicpanel and/or a photovoltaic panel operatively attached to a electronicmodule which includes for instance a DC-to-DC converter. The term“electronic module” and “photovoltaic module” are used hereininterchangeably and refer to a functional electronic circuit attached toa photovoltaic panel.

The term “noise” as used herein in a communication channel, includes anyunwanted signal finding itself in the communication channel. Sources ofnoise may include radio frequency interference (RPI), mains electricityhum, unsuppressed switching voltages and crosstalk.

The term “crosstalk” as used herein refers to any phenomenon by which asignal transmitted on a cable, circuit or channel of a transmissionsystem creates an undesired effect in another cable, circuit or channel.Crosstalk is usually caused by undesired capacitive, inductive, orconductive coupling from one cable, a circuit, part of a circuit, orchannel, to another.

The term “telemetry” as used herein refers to measurement, transmissionand reception of data by wire, radio, or other means from remotesources. In the context of the present invention, telemetries are fromthe photovoltaic panels.

The term “transducer” as used herein refers to a device used for theconversion of one type of energy to another, for example, the devicechanges electrical energy in to electromagnetic energy and vice versa.The term “transducer” herein may also have functions of a sensor ordetector. The terms “sensor” and “transducer” as used herein are usedinterchangeably.

The terms “signal”, “signaling” or “signaling mechanism” as used hereinrefers to a signal modulated on a carrier signal. The carrier signal maybe an electrical or an electromagnetic signal. The signal may be asimple on/off signal or a complex signal which imparts information asdata. For a modulated signal, the modulation method may be by any suchmethod known in the art, by way of example, frequency modulation (FM)transmission, amplitude modulation (AM), FSK (frequency shift keying)modulation, PSK (phase shift keying) modulation, various QAM (quadratureamplitude modulation) constellations, or any other method of modulation.Although strictly, the terms “modulation” and “coding” are notequivalent, the term modulation and demodulation are typically usedherein to include coding and decoding respectively.

The term “signal strength” as used herein refers to the magnitude of theelectric field/current or voltage at a reference point that is asignificant distance from a transmitting source. Typically, “signalstrength” is expressed in voltage per length or signal power received bya reference point expressed in decibel (dB) per length (meter),dB-millivolts per meter (dBmV/m), and dB-microvolts per meter (dBμV/m)or in decibels above a reference level of one milliwatt (dBm).

The term “positive comparison” in reference to the comparison of twocodes or two signals means equal within tolerances or thresholds orderivable one from the other in a known way.

BRIEF SUMMARY

According to the present invention there is provided a method ofsignaling between a photovoltaic module and an inverter module. Theinverter module is connected to the photovoltaic module. In an initialmode of operation an initial code is modulated to produce an initialsignal. The initial signal is transmitted from the inverter module tothe photovoltaic module. The initial signal is received by thephotovoltaic module. The operating mode is then changed to a normal modeof power conversion, and during the normal mode of operation a controlsignal is transmitted from the inverter to the photovoltaic module. Acontrol code is demodulated and received from the control signal. Thecontrol code is compared with the initial code producing a comparison.The control command of the control signal is validated as a validcontrol command from the inverter module with the control command onlyacted upon when the comparison is a positive comparison. Current outputof photovoltaic modules may be limited during the initial mode ofoperation. The initial code is typically saved in a memory. Modulatingthe code may be performed by varying the input impedance of the invertermodule to produce a variation in voltage or current at the output of thephotovoltaic module. The photovoltaic module senses the variation involtage or current at the output of the photovoltaic module. Respectivesignal strengths for the initial signal and the control signal may bemeasured. The signal strengths are compared to produce a comparisonresult. When the comparison result is greater than a previously storedthreshold value then an alarm is set or the control command isinvalidated. Fluctuations prior to measuring the signal strength arepreferably filtered out. Electrical energy is typically stored forsupplying power for the varying and the sensing.

According to the present invention there is provided a photovoltaicgeneration system with a photovoltaic module including a firsttransceiver connected to the DC power line. A load module is connectedto the DC power line. The load module including a second transceiver isconnected to the DC power line. There is a pairing mechanism and asignaling mechanism between the first and second transceivers. Based onthe pairing mechanism, another photovoltaic module or another loadmodule in the photovoltaic generation system is excluded from signalingwith either the photovoltaic module or the load module. A charge storagedevice may be included within the photovoltaic module adapted to storecharge and supply power to the photovoltaic module. A secondphotovoltaic module may be attached to the photovoltaic module alongwith a second signaling mechanism adapted to signal between thephotovoltaic module and the second photovoltaic module. The signalingmechanism is typically configured to signal controls to the secondphotovoltaic module by relaying commands through the second signalmechanism. The signaling mechanism may also be configured to monitor thesecond photovoltaic module by receiving telemetries through the secondsignal mechanism. A transducer is optionally connected to the DC powerline and the first transceiver to modulate/demodulate a signal onto/fromsaid power line and a sensor may be connected to the DC power line andthe second transceiver to demodulate/modulate the signal from/onto saidpower line. In an initial mode of operation, an initial signal from theload module is transmitted to the photovoltaic module and an initialcode is demodulated by the photovoltaic module. In a subsequent normalmode of operation the initial code is used to validate a control commandfrom the load module. A memory may also be included within thephotovoltaic module, the memory preferably adapted to store the initialcode.

The foregoing and/or other aspects will become apparent from thefollowing detailed description when considered in conjunction with theaccompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1a shows a power generation circuit according to an embodiment ofthe present invention.

FIG. 1b shows further details of a transceiver attached to the output ofphotovoltaic modules in the power generation circuit shown in FIG. 1aaccording to an embodiment of the present invention.

FIGS. 1c and 1d illustrate respective methods of modulation anddemodulation according to aspects of the present invention.

FIG. 1e shows further details of a control and communications unitattached to the load shown in FIG. 1 a, according to features of thepresent invention.

FIG. 2 shows a method according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below to explain the presentinvention by referring to the figures.

It should be noted, that although the discussion herein relatesprimarily to methods in photovoltaic systems, the present invention may,by non-limiting example, alternatively be configured as well using otherdistributed power systems including (but not limited to) wind turbines,hydro-turbines, fuel cells, storage systems such as battery,super-conducting flywheel, and capacitors, and mechanical devicesincluding conventional and variable speed diesel engines, Stirlingengines, gas turbines, and micro-turbines.

It should be noted that although embodiments of the present inventionare described in terms of an inverter as a load, the present inventionmay be applied equally well to other loads including non-grid tiedapplications such as battery chargers and DC-DC power converters.

Before explaining embodiments of the invention in detail, it is to beunderstood that the invention is not limited in its application to thedetails of design and the arrangement of the components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments or of being practiced or carried out invarious ways. Also, it is to be understood that the phraseology andterminology employed herein is for the purpose of description and shouldnot be regarded as limiting.

The term “pairing or paired” as used herein refers to at least two powergeneration system components such as an inverter on one side, and on theother side photovoltaic panels and/or electronic modules which are“paired” or associated with each other. “Pairing” establishes anassociation between an inverter and a particular set of one or morephotovoltaic panels and/or electronic modules. The “pairing” betweenpower generation components is typically performed via initialassignment of codes and storage within each power generation component.The “pairing” process may take place at the time of manufacture of powergeneration system components, during installation of a power generationsystem, during the operation of the power generation system and/or afteran upgrade/modification to the power generation system. The storage ofcodes typically establishes the electrical connections and futurecommunication protocols of signaling.

Referring now to the drawings, reference is now made to FIG. 1a whichshows a power generation circuit 101 according to an embodiment of thepresent invention. Two photovoltaic strings 120, by way of example, areconnected in parallel to an inverter 150. Details of only one of strings120 are shown explicitly. In each of strings 120, direct current powersources 116 are serially connected. Each direct current power source 116includes a photovoltaic panel 100 connected to an electronic module orphotovoltaic module 102. Outputs of photovoltaic modules 102 areconnected in series to form serial string 120. Photovoltaic modules 102may be direct current (DC) to DC converters such as a buck circuit,boost circuit, buck/boost or buck+ boost circuit or any other knownswitching converter topology Attached to photovoltaic modules 102 is aprocessor 132 which accesses a memory 130. A transceiver 108 is attachedto the output of electronic module 102 and to processor 132. Accordingto a feature of the present invention, one of photovoltaic modules 102referenced 102 a is a master electronic module 102 a of string 120 andcontrols and communicates with the other modules, i.e. slave modules 102via power line communications or wireless link.

Load 150 is typically a direct current (DC) to alternating current (AC)inverter. String 120 attaches across the input of load 150. The outputof load 150 is typically attached to an AC grid voltage. Attached toload 150 is inverter module 104. Inverter module 104 contains a memorymodule 110, transceiver 118 and control unit 112. Inverter module 104 isattached to load 150 with bi-directional connection 114. Transducer 106is attached to the power connection to load 150 and provides a signal toinverter module 104.

Reference is now made to FIG. 2 which shows a method 201 according to anembodiment of the present invention. Method 201 mitigates thedetrimental effects of crosstalk in the communication channel along thepower lines connecting photovoltaic modules 102 with inverter module104. Method 201 illustrates two modes of operation, the first mode ofoperation is an initial mode 300 and the second mode of operation is anormal mode 500 during which there is normal conversion of power. At thebeginning of initial mode 300, current limiting (step 400) typicallylimits the DC current output of each electronic module 102. The limitedDC current output of each module 102, prevents for example, thesituation where the entire load 150 current (h) is being supplied by asingle string 120 or some strings are not providing any of the loadcurrent (h).

An initial code stored in memory 110 modulates (step 202) a variation ofvoltage or current on the input of load 150 to produce an initialsignal. The initial signal is transmitted (step 203) from invertermodule 104. Direct electrical variation of current on the input of load150 may be achieved by using control line 114 to vary the inputimpedance of load 150 according to a code previously stored in memory110. The frequency of the transmitted control signal may be between 1 Hzand 100 Hz or may also be at higher frequencies.

The initial signal transmitted (step 203) from inverter module 104 isthen received (step 205) by electronic module 102. The initial signal issensed and a measure of the signal strength of the initial signal may beperformed. The measure of the signal strength of the initial signal maybe stored in memory 130. The initial signal is demodulated and/ordecoded (step 206) by transceiver 108 and the initial code correspondingto inverter module 104 is obtained from the demodulated output voltage.The initial code corresponding to inverter module 104 is stored (step207) in memory 130.

In order to end initial mode of operation in decision box 209, a controlsignal is typically modulated (step 210) and transmitted (step 211) frominverter module 104. The control signal is received (step 213) anddemodulated and/or decoded (step 214) by photovoltaic module 102 and acontrol code is stored. In decision box 215, the control code iscompared with the initial code and if the comparison is positive, i.e.the control code is the same as the initial code, then electronic module102 validates the command as coming from inverter module104 with whichphotovoltaic module 102 is paired and not a control signal as crosstalkfrom another inverter module in the same photovoltaic generation field.In decision box 215, if the initial code positively compares with thecontrol code normal conversion of power (step 502) commences. An MPPcircuit performs maximum peak power tracking (MPPT), in which thecurrent extracted from a photovoltaic panel provides the maximum averagepower (i.e., if more current is extracted, the average voltage from thepanel starts to drop, thus lowering the harvested power). Itcontinuously monitors the current and voltage provided by the panel anduses one of several well-known MPP tracking algorithms to maintainmaximum possible power output. Maximum peak power tracking (MPPT)continuously tracks the PV's power output to determine an optimalworking point for maximum power.

As an example, of a control signal is a keep alive signal 550. When keepalive signal is encoded with a valid control code then photovoltaicmodule 102 maintains normal conversion of power. Otherwise, if keepalive signal 550 is not encoded with a valid control signal, such as ifthe signal received is “pick-up” or cross talk from another inverter inthe photovoltaic field then in decision box 215 keep alive signal 550 isnot validated and photovoltaic module 102 enters initial mode 400 whichis typically a safety or current limited mode of operation until a validkeep alive signal 550 signal is received to enter normal operation 500.

There may be multiple possible frequencies for communication, and duringpairing (initial mode 300) the initial signal transmitted to andreceived by photovoltaic module 102 may specify to photovoltaic module102 which frequencies to listen to and to transmit on.

Signal strength may be also be used alternatively or in addition toinvalidate a control signal or at least set an alert condition.Typically, signal strength variation as measured by photovoltaic module102 from a transmission from inverter module 104 is not expected to varymore than a threshold ±3 decibel (dB). A variation of signal strengthmore between the initial transmission (step 203) and the controltransmission (step 211) greater than the threshold may set an alarmcondition or be used alternatively or in addition to invalidate acontrol signal in decision box 215 as being sourced by an unpairedinverter module 104.

Reference is now also made to FIG. 1b which illustrates schematicallyfurther details of power source 116, according to an embodiment of thepresent invention. The DC output of power source 116 is connected to acharge storage device 300 a. Charge storage device 300 a has a directcurrent (DC) output which supplies power to a modulator/demodulator unit302 a. A transducer/sensor 1106 attached to the output of module 102connects to modulator/demodulator 302 a.

Modulator/demodulator unit 302 a has a bi-directional connection tomemory 130 and/or processor 132 for storing a (de)modulation voltageV_(m) or a code decoded from an input signal. The DC output of chargestorage device 300 a may provide processor 132 and memory 130 with DCpower. Charge storage device 300 a is typically a battery or a capacitorwhich is charged via the DC output of module 102 during daytimeoperation of power circuit 101. The charge stored in storage device 300a during daytime may be used at nighttime.

Reference is now made FIG. 1e which shows further details of invertermodule 104 attached to load 150 in power generation circuit 101according to an embodiment of the present invention. The output of load150 is connected to an AC grid voltage. The AC grid voltage is connectedto charge storage device 300 b. Charge storage device 300 b is typicallya battery or a capacitor which is charged via the rectified grid voltageon the output of load 150 and/or from the DC input to load 150 duringdaytime operation. Charge storage device 300 b has a direct current (DC)output which supplies power to modulator/demodulator unit 302 b.Transducer 106, connected at the input of load 150, is connected tomodulator/demodulator unit 302 b. Modulator/demodulator unit 302 b alsohas a connection to memory 110 or control unit 112. Control unit 112 isattached to memory 110. Control unit 112 is attached to load 150 viacontrol line 114. The DC output of charge storage device 300 b mayprovide control unit 112 and memory 110 with DC power.

Reference is now made to FIG. 1e which shows a method 103 used tooperate transceiver 108/118 according to different aspects of thepresent invention.

The transmission of the control signal from inverter module 104 ispreferably performed by transceiver 118 with method 103. Thetransmission of telemetries by photovoltaic module 102 is by transceiver108 with method 103. When photovoltaic module 102 sends telemetries, asource identification code identifying the photovoltaic module 102 asthe source and a destination identification code identifying invertermodule 104 as the destination may be included in the communicationsignal.

When transceiver 108/118 is operating as a transmitter, modulator 302a/302 b causes a modulated signal to be superimposed (step 107) on tothe DC power line. Modulator 302 a/302 b has an input voltage (V_(m))which causes a current (I_(m)) to be drawn (step 105) from chargestorage device 300 a/300 b which in turn draws current from the outputof module 102 and from the input of load 150 respectively. The currentdrawn from charge storage device 300 a/300 b is therefore a function ofthe input voltage i.e. modulating voltage (V_(m)). The superposition(step 107) of the modulated signal on to the DC power line is preferablyvia transducer 106/1106 or by a direct electrical connection (i.e. via acoupling capacitor) to the DC power line.

According to an exemplary embodiment of the present invention, thetransmission of the control signal from inverter module 104 isoptionally performed without the use of transducer 106. Instead themodulated control signal is made by altering of the input impedance ofload 150 according to a code in memory 110 via control line 114. Thevariation of the input impedance of load 150 causes the DC input currentof load 150 (drawn from modules 102) to vary by virtue of Ohm's law. Thedrawn current from modules 102 is sensed by transducer 1106 andde-modulated by transceiver 108 in module 102.

Reference is now made to FIG. 1d which shows a method 109 used tooperate transceiver 108/118 according to an aspect of the presentinvention. The reception of telemetries by inverter module 104 isperformed by transceiver 118 with method 109.

The reception of the control signal from inverter module 104 byphotovoltaic modules 102 is performed by transceiver 108 with method109. When transceiver 108/118 is operating as a receiver a signalpresent on the DC power line is extracted (step 111) from the DC powerline via transducer 106/1106 or by direct electrical connection (i.e.via coupling capacitor). Demodulator 302 a/302 b de-modulates the sensedsignal present on the DC power line. In demodulation, the signal sensedand extracted (step 111) from the DC power line may vary (step 113) thecurrent (I_(m)) drawn from charge storage device 300 a/300 b which inturn draws current from the output of module 102 and from the input ofload 150 respectively to produce a demodulated output voltage V_(m). Thedemodulated output voltage (V_(m)) is a function of drawn current I_(m).

While the invention has been described with respect to a limited numberof embodiments, it will be appreciated that many variations,modifications and other applications of the invention may be made.

1-16. (canceled)
 17. A method comprising: configuring a photovoltaiccontrol circuit for controlling an output from a DC power source tolimit current from the output; configuring a central control circuit forpairing with the photovoltaic control circuit, wherein the configuringcomprises: receiving control data from the central control circuit; andvalidating that the control data comes from the central control circuit;and configuring the photovoltaic control circuit to, in response to thevalidating the control data, provide the current on the output.
 18. Themethod of claim 17, wherein the receiving the control data comprisesreceiving configuration data including initialization data.
 19. Themethod of claim 18, wherein the validating the control data comprisesestablishing electrical connections and future communication protocols.20. The method of claim 17, wherein the controlling the output from theDC power source comprises, in response to a failed validation of thecontrol data, limiting the current from the output.
 21. The method ofclaim 17, wherein the providing the current on the output furthercomprises using a maximum peak power tracking circuit.
 22. The method ofclaim 17, wherein the receiving the control data comprises monitoringkeep alive data.
 23. The method of claim 22, wherein the monitoring thekeep alive data comprises: validating that the central control circuitgenerates the keep alive data; and based on the validation, providingthe current on the output.
 24. The method of claim 23, furthercomprising configuring the photovoltaic control circuit to, upon notreceiving the keep alive data or upon a failed validation of the keepalive data, limit the current from the output.
 25. The method of claim18, wherein the initialization data is transmitted at a firstcommunication frequency and keep alive data is transmitted at a secondcommunication frequency.
 26. The method of claim 25, wherein the secondcommunication frequency is higher than the first communicationfrequency.
 27. The method of claim 26, wherein the first communicationfrequency is between 1 Hz and 100 Hz.
 28. The method of claim 25,wherein the initialization data includes an indication of the secondcommunication frequency.
 29. The method of claim 25, wherein the secondcommunication frequency is one of a plurality of frequencies used in aFrequency Shift Keying modulation scheme.
 30. The method of claim 17,wherein the validating the control data comprises comparing a signalstrength of the control data to a threshold.
 31. The method of claim 30,further comprising configuring the threshold according to a signalstrength of initialization data.
 32. The method of claim 17, furthercomprising configuring the photovoltaic control circuit to transmit atelemetry message to the central control circuit.
 33. The method ofclaim 18, further comprising configuring the central control circuit toinclude an inverter and to output the initialization data from theinverter based on a modulation varying in accordance with an inputparameter of the inverter.
 34. The method of claim 33, wherein themodulation occurs at a frequency between 1 Hz and 100 Hz.
 35. The methodof claim 34, wherein the modulation comprises varying an input impedanceof the inverter.
 36. The method of claim 34, wherein the modulationcomprises varying an input voltage of the inverter.
 37. The method ofclaim 34, wherein the modulation comprises varying an input current ofthe inverter.
 38. The method of claim 37, further comprising configuringthe photovoltaic control circuit to demodulate an initial control signalresponsive to the input current of the inverter.
 39. An apparatuscomprising: a photovoltaic control circuit, wherein the photovoltaiccontrol circuit is configured to: control an output from a DC powersource to limit current from the output; receive control data from acentral control circuit; validate that the control data comes from thecentral control circuit; and provide, based on the validation, thecurrent on the output; and the central control circuit paired with thephotovoltaic control circuit, wherein the central control circuit isconfigured to transmit the control data to the photovoltaic controlcircuit.
 40. The apparatus of claim 39, wherein the photovoltaic controlcircuit is further configured to monitor, based on receiving the controldata, keep alive data.
 41. The apparatus of claim 40, wherein thephotovoltaic control circuit is further configured to: validate that thecentral control circuit generates the keep alive data; and based on thevalidation, provide the current on the output.
 42. The apparatus ofclaim 41, wherein the photovoltaic control circuit is further configuredto, based on not receiving the keep alive data or on a failed validationof the keep alive data, limit the current from the output.
 43. A methodcomprising: generating, from initialization data, an initializationsignal, wherein the generating comprises modulating a first voltage or afirst current at an input of a direct current (DC) to alternatingcurrent (AC) inverter; generating, from control data, a control signal,wherein the generating comprises modulating a second voltage or a secondcurrent at the input of the DC-to-AC inverter; receiving, by aphotovoltaic control circuit and from a central control circuit, thecontrol data and the initialization data; comparing, by the photovoltaiccontrol circuit and based on demodulating the initialization signal andthe control signal, the initialization data to the control data; andproviding, by the photovoltaic control circuit and based on theinitialization data matching the control data, current on an output froma DC power source.
 44. The method of claim 43, further comprising:determining, by the photovoltaic control circuit, that theinitialization data does not match the control data; and limiting, bythe photovoltaic control circuit and based on the determining, thecurrent on the output from the DC power source.
 45. The method of claim43, further comprising validating, by the photovoltaic control circuit,that the control data comes from the central control circuit.
 46. Themethod of claim 45, further comprising limiting, by the photovoltaiccontrol circuit and based on a failed validation, the current on theoutput from the DC power source.